Conventionally, a technology of conveying substrates such as wafers for manufacturing semiconductors by a robot is used broadly. Here, various processing steps such as a wafer cleaning process, a film-forming process, a heating process, and an etching process are executed when manufacturing semiconductors. The respective processing steps are executed by different processing devices respectively, and therefore wafers need to be conveyed among a plurality of processing devices.
A robot is used for the above-mentioned wafer conveyance and high cleanliness is required for the surrounding atmosphere in the semiconductor manufacturing process. Therefore, the benefit of an unmanned operation by using a robot is great.
Additionally, in order to improve throughput of the semiconductor manufacturing, tact time upon conveying wafers is required to be shortened. There is a robot conveying a plurality of wafers at the same time by one hand mounted on a robot arm as a technology for shortening the tact time upon conveying wafers. This kind of robot, for example, holds and takes a plurality of wafers at the same time by one hand from a lot of wafers stored in a FOUP and conveys them to a wafer placing shelf on a processing device side at the same time (Patent Document 1).
Note that, in various processing steps upon manufacturing semiconductors, there are a step of processing a plurality of wafers at the same time (batch processing step) and a step of processing wafers one by one (single-wafer processing step). When conveying wafers in relation to the batch processing step, the above-mentioned robot which conveys a plurality of wafers at the same time is suitable.
In contrast, when conveying wafers in relation to the single-wafer processing step, the processing step is executed for each wafer. Therefore, it may be advantageous to convey processed wafers and un-processed wafers one by one respectively. In this case, the above-mentioned robot which conveys a plurality of wafers at the same time is not suitable.
In Patent Document 2, a substrate holding device including a pair of hands (U-shaped blade members) capable of changing their interval in the vertical direction is described as a technology for carrying-out one processed substrate and carrying-in one unprocessed substrate at the same time. In this substrate holding device, by widening a vertical interval between hands when the lower hand is in a wafer holding state and the upper hand is in a wafer non-holding state, a wafer held by the lower hand can be placed onto an empty lower stage of a shelf and the empty upper hand can receive a wafer placed on an upper stage of the shelf at the same time.